Field of the Invention
The present invention relates to prediction of the remaining amount of a consumable material in an image forming apparatus such as an electrophotographic printer.
Description of the Related Art
Electrophotographic image forming apparatuses have an optical scanning unit for exposing a photosensitive member. The optical scanning unit emits laser light based on image data, reflects the laser light with a rotating polygon mirror, and causes the laser light to pass through a scanning lens, so as to irradiate and expose the photosensitive member. Scanning is performed in which a laser light spot formed on the surface of the photosensitive member is moved by rotating the rotating polygon mirror, whereby a latent image is formed on the photosensitive member.
The scanning lens is a lens having so-called an fθ (f-theta) characteristic. The fθ characteristic is an optical characteristic according to which the laser light forms an image on the surface of the photosensitive member, such that the laser light spot on the surface of the photosensitive member moves at a constant speed over the surface of the photosensitive member when the rotating polygon mirror is rotating at a constant angular velocity. Appropriate exposure can be performed by using the scanning lens having the fθ characteristic in this manner.
Such a scanning lens having the fθ characteristic is relatively large and expensive. Therefore, for the purpose of reducing the size and cost of the image forming apparatus, it has been considered to not use a scanning lens itself, or to use a scanning lens that does not have the fθ characteristic.
Japanese Patent Laid-Open No. 58-125064 discloses that electrical correction is performed so as to change an image clock frequency while one scanning operation is performed, such that even in the case where a laser light spot on the surface of the photosensitive member does not move at a constant speed over the surface of the photosensitive member, dots formed on the surface of the photosensitive member have a certain width.
Also, Japanese Patent Laid-Open No. 2002-72770 discloses a technique for obtaining image density information by counting (pixel counting) the presence/absence of an image signal every pixel at a predetermined frequency, and using the obtained image density information for estimating the consumption amount of a developing agent or the like.
However, if a conventional counting method is used in an image forming apparatus that performs scanning in a main scanning direction at a scanning speed that is not constant, there is a possibility that the accuracy for estimating the consumption amount deteriorates due to an error that occurs between the consumption amount of a developing agent that is actually consumed and the consumption amount of the developing agent that is obtained from the count value.